To over-top the neighbors, shade-intolerant plants trigger shade avoidance responses with increasing the elongation of stem-like organs at the expense of leaf development. Shade-induced elongation growth has been extensively studied, while the regulatory mechanisms underlying shade-suppressed leaf development remain poorly understood. Here we find sucrose can rescue shade-inhibited leaf development, which requires the functions of phytochrome A (phyA) and TARGET OF RAPAMYCIN (TOR) complex. We confirm an interaction between PHYA and LETHAL WITH SEC THIRTEEN 8 (LST8), a component of TOR complex. Shade and phyA affect TOR activity, in turn TOR affects the protein stability of PHYA. The sucrose–TOR mediated accumulation of PHYA requires CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1)/SUPPRESSOR OF PHYA-105 (SPA) complex. Transcriptome analysis further reveals that sucrose and phyA regulate the expression of leaf development-related genes under shade, particularly those involved in cytokinin metabolism. Our work uncovers a critical role for TOR and PHYA in linking light signaling with cellular energy status, a mechanism that fine-tunes leaf development specifically under shade conditions. Shade limits leaf growth. Here, Wang et al. show that sucrose alleviates shade-repressed leaf development by activating TOR and stabilizing PHYA, thereby regulating cytokinin and leaf development-related genes.
Wáng et al. (Tue,) studied this question.